2016/01/16

DISCLAIMER: These notes are from the defunct k8 project whichprecedes SquirrelJME. The notes for SquirrelJME start on 2016/02/26!The k8 project was effectively a Java SE 8 operating system and as suchall of the notes are in the context of that scope. That project is nolonger my goal as SquirrelJME is the spiritual successor to it.

11:29

Not sure if I need to output anything else for the Java instruction dump to
the manifests.

11:48

And now to redump the PowerPC manifests so that it matches the newer format
and has the image const and value set (which is for decoding).

13:20

Well the new field layout is much more compact and probably easier to
understand.

14:58

The joys of distributed version control where you have the entire history.
Going back in time has been quite helpful too. Now I have the new stuff for the
instructions so I can continue on the refactor of ArchitectureData. I do
wonder though if it would be possible for me to keep a map which bases the key
on the value. I could make a special map type for that, it would require
loading of the manifest to determine the name of the instruction however. But
before I do that I will need to cleanout the Java and PowerPC code.

15:16

I wonder if I can split off java.net or at least have two new packages to
make the jump lighter. Appears I will need to split off URI/URL. Then I can
have the socket based stuff in java.nio go into the net package. There would
be a splice between them, however it would split them even further apart. I
need to look at InetAddress though since the SecurityManager uses that.

15:26

I can actually split off java.math. Actually no I cannot due to a few
imports due to Java 8's streams.

16:33

I believe I will have to fork POIT to fixup for these new changes.

16:46

I could attempt writing up NARF with some of the stuff I learned from POIT.
POIT will generate very bloated code for the most part even for the simplest
of methods. However, SSA is insanely complex.

16:57

Perhaps I can use a threading approach. Basically the entire layout of the
method will be placed and operands and their register usages will be determined
and stored. Instructions will have a flow back (dependency) and used local and
stack variables would have a usage and liveness so to speak.

17:05

Actually for thrown exceptions, the only odd time they are thrown is during
potentially very fatal virtual machine failures. However for speed, my virtual
machine should just read from null pointers and such (except if there is no
MMU available, it must check them) so that a trap in the CPU is triggered and
then where an exception is generated, rather than just checking for null
pointers. A check against a null pointer can just be a dereference of the
pointer, I do not really have to do anything with it. Of course though, the
first page of memory must not be writable, however if a system needs it it is
possible to have a null pointer which is NOT zero.

17:20

Actually instead of having register shuffling to that their numbers are dynamic
to the code running, there could instead be virtual registers which map to real
registers and stack locations. So basically something such as this:

The stack
-------------------------
sjl1 Save area for Java local variables on the CPU stack.
sjl* ...
sjs1 Save area for Java stack variables on the CPU stack.
sjs* ...

So essentially, a Java operation which performs on stack entries will have a
modifiable (if needed) link to a Java local/stack. The code in POIT already
has a fixed location for locals and stack items however it is very fixed in
that temporaries are needed if the stack/local is really large. However, using
a kind of pointer system, registers would be saved into their local/stack
positions so that if an exception is thrown or a method call is returned from,
it can just load from the saved position as needed. The only thing though is
that having the registers caller save would be better, however the positions
of entries on the stack/locals might not be known to methods being called (they
would be unable to know the size of the stack/locals). There are the method
table of contents however. But my point is that if a method is called and it
wants to save r17 because it overwrites the value, it would have no idea
where to store that value before the method call is done. So to simplify the
handling of this, before all methods (or null pointers are dereferenced) the
registers which are active will have to be saved and restored. Otherwise if
they are not saved, then on the handling of an exception values of locals will
have incorrect values.

17:31

Now say if there is a jump back from a later instruction to an earlier
instruction. SSA would demand using phi and require more complex parsing to
be done. However for simplicity I can generate code which performs a jump call
back to reload the required registers to the correct locations for the target
block before jumping to it. This way, when the code is first entered that is
not done because things are normal. Essentially it would be like this as an
example:

// Block of code is entered at this point
_entry1:
instruction 1
instruction 2
instruction 3
if foo, jump to _prejumpentry1
instruction 4
instruction 5
return
_prejumpentry1:
move around links before the jump is made
jump to _entry1

Exceptions would be sort of similar if they jump, however the dispatcher which
determines the exception for handling will determine the point in the code to
jump at. Then the entry of the exception handler would setup the required state
needed to run the code properly.

17:57

For complex methods that are gigantic this might produce some bad code, but the
general Java practice is to make smaller methods rather than gigantic ones.
Most of Foobarniux so far just consists of simple methods except for few
methods that may be quite large since they have not been refactored. I suppose
the first step would be to load all the instructions so that I know what they
are, then assign native operations and registers to them as required.

23:06

Tried to sleep after eating a bunch of food, but really could not before so now
I am more awake again.

23:34

To simplify dynamic recompiler service lookup, I can just have a foo@arch
which can simplify things. If one is not found or does not support a config
then it will fallback to another class. This will remove the need of setting
up sub-services and such, which can get bothersome and boilerplated.